12 Common Furnace Pilot Light Problems and Solutions

The following are the 12 most frequent causes of furnace pilot light issues in Los Angeles homes, along with practical ways to fix them safely.

1. Dirty Thermocouple

A dirty thermocouple is a common cause of the pilot light going out, as it can’t detect the pilot flame and shuts off the gas valve. When this happens, the burners won’t stay lit, and the furnace blows only cold air.

Troubleshooting

Turn off the power and gas to the furnace. Open the front panel and find the small copper rod next to the pilot flame. If the tip appears dark, sooty, or covered in residue, buildup is likely blocking heat detection.

Solution

Use a piece of fine sandpaper or steel wool to clean the thermocouple tip until it shines. Then reattach it firmly. Relight the pilot light following the label on your furnace. If the flame stays on, the sensor is working again. If it goes out, replace the thermocouple with a compatible part from your furnace brand.

2. Loose Thermocouple Connection

A loose thermocouple connection weakens the electrical signal to the gas valve, cutting gas flow even if the pilot flame is strong. This often causes flickering or sudden pilot shutdowns.

Troubleshooting

Turn off the furnace and let it cool. Follow the thermocouple wire to where it connects to the gas valve. Wiggle the wire gently if it moves or feels loose; that’s the problem.

Solution

Tighten the nut using a wrench, turning it only a quarter turn after it’s snug. Avoid over-tightening, which can crack the fitting. Turn the gas back on and test the furnace pilot light again.

3. Weak Pilot Flame

A weak or yellow pilot flame means your furnace isn’t getting enough gas or oxygen. This makes the flame unstable and unable to heat the thermocouple. 

Troubleshooting

Look through the pilot window. A healthy pilot flame should be steady and blue with a small yellow tip. If it’s small, orange, or flickering, check for dust around the pilot opening.

Solution

Use a can of compressed air or a small brush to clean the area. Check that nearby vents aren’t blocked. Make sure your gas shutoff valve is fully open. If the flame still looks weak, the gas pressure may be low and should be checked by your utility company. 

4. Faulty Gas Valve

A faulty gas valve can prevent the pilot light from working by restricting fuel flow or failing to open when signaled. The burners will never ignite, leaving you with no heat.

Troubleshooting

Check if the valve handle is set to “On.” Then, while the furnace tries to start, listen for a faint click that’s the valve opening. If you hear nothing, the internal mechanism might be stuck.

Solution

Gently tap the valve body with the handle of a screwdriver to loosen debris inside. Never force it open. If the pilot light still won’t light, the valve likely needs replacement. Gas valves require correct pressure calibration, so have a pro replace them using brand-approved parts.

5. Drafts Blowing Out the Pilot

Strong airflow or drafts around the furnace can blow out the pilot flame, especially in basements, garages, or utility rooms with open vents. This issue is more common in older Los Angeles homes with unsealed air gaps.

Troubleshooting

Light an incense stick and hold it near the pilot area with the system off. If the smoke moves or blows to the side, it indicates that air is entering the space.

Solution

Seal cracks in walls and around ductwork using foil tape or silicone caulk. Close nearby doors and windows. Avoid storing fans or running large exhaust systems near the furnace. Once the draft is gone, relight the pilot light and watch that it stays steady.

6. Clogged Pilot Orifice

A clogged pilot orifice blocks gas from reaching the pilot flame, causing a weak or nonexistent flame even when the gas valve is open. Dust and rust buildup from years of use are the usual culprits.

Troubleshooting

Turn off the gas and unscrew the small pilot tube using a wrench. Hold it up to the light. If you can’t see through it, it’s blocked.

Solution

Use a fine needle or brush to clear the hole, then blow compressed air through the tube. Reinstall it and turn the gas back on. When you relight the furnace pilot light, it should produce a clear, steady blue flame.

7. Faulty Igniter or Spark Electrode

If your furnace has electronic ignition instead of a standing pilot light, a faulty igniter or spark electrode will prevent ignition altogether. You’ll hear clicks without seeing a flame.

Troubleshooting

Shut off the power. Remove the front panel and find the igniter near the burners. Look for cracks, white buildup, or frayed wires.

Solution

Clean off dust using a soft brush. If you notice damage or heavy residue, replace the igniter. Carrier and American Standard furnaces use silicon nitride or silicon carbide igniters, which must match your model’s part number exactly.

8. Low Gas Pressure

Low gas pressure can cause your furnace pilot light to go out or burn weakly, leading to incomplete combustion and poor heating performance. This can also cause your energy bills to rise.

Troubleshooting

Check another gas appliance, like your stove, to see if the flame looks smaller than usual. If multiple appliances are affected, the problem is with your main gas supply.

Solution

Call your gas provider to check and restore proper line pressure. Inside the furnace, make sure the gas valve regulator screw hasn’t shifted. Only a certified technician should adjust pressure settings, but you can confirm that all valves in the line are fully open.

9. Faulty Control Board or Safety Switch

A faulty control board or safety switch cuts off signals to the igniter and gas valve, preventing the pilot flame from lighting. This is more common in newer electronic ignition furnaces.

Troubleshooting

Look for flashing lights on the board. Use your manual to match the code pattern. Some systems also trip a rollout switch if overheating occurs.

Solution

Turn off the power for 30 seconds, then turn it back on to reset the board. If the same error returns, remove dust with a soft brush. Replace the fuse on the board if it is blown. Persistent problems may mean the board itself needs replacement.

10. Moisture or Condensation Around the Pilot Assembly

Water leaks or condensation near the pilot assembly can cool the flame and corrode nearby parts, leading to short cycling or complete shutdown. This happens when furnaces sit near humidifiers or drain lines.

Troubleshooting

Inspect the bottom of the furnace for puddles, rust stains, or water marks. Trace any moisture to its source.

Solution

Wipe the area dry and tighten loose humidifier lines. Place a drip pan or small barrier between the humidifier and pilot assembly. If corrosion is visible, have a technician inspect the wiring and flame sensor.

11. Dirty Air Filter Restricting Combustion Air

A dirty air filter restricts airflow and starves the pilot flame of oxygen, causing it to flicker or die. It can also make the furnace overheat and shut down.

Troubleshooting

Remove the filter and hold it up to a light source. If light doesn’t pass through, it’s too dirty.

Solution

Replace it with the correct MERV-rated filter. A clean filter improves airflow and helps the furnace pilot light stay stable. Set reminders to change filters every 30 days during heavy use.

12. Electrical or Power Interruption to the Furnace

Power interruptions or tripped breakers can cut off power to the control board or gas valve, causing the furnace pilot light to not work properly.

Troubleshooting

Check the wall switch that controls your furnace power – it’s often mistaken for a light switch. Inspect your home’s electrical panel for tripped breakers or a blown fuse.

Solution

Reset the breaker once. If it trips again, there may be a wiring issue or an overloaded circuit. Replace the furnace’s internal fuse if it has burned out. Keeping the system on a dedicated circuit helps prevent future outages.